How to modify a column named in another column using adjacent column in tidyverse?

Question

I've the following dataframe,

df <- tibble(x = c(2, 3, 4)) %>% 
mutate(`1` = 99, `2` = 88, `3` = 77, `4` = 66, `5` = 55)

column x holds the column names which needs to be manipulated, the value in that column has to be replaced with the sum of values in columns x-1, x and x+1. For example, for the first row where x is 2, value in column 2 has to be replaced with (99+88+77) = 264.

I tried using double curly brackets({{}}) and :=, like below,

df %>% 
  mutate("{{x}}" := {{x-1}} + {{x}} + {{x+1}})

but I'm getting the following error, Error in local_error_context(dots = dots, .index = i, mask = mask) : promise already under evaluation: recursive default argument reference or earlier problems?

Then I tried accessing the column using cur_column() inside across() like below,

df %>% 
  mutate(across(-x, ~if_else(x == cur_column(), {{cur_column()}}, .x)))

and I'm getting the same error as above, I think I may be using the curly operator incorrectly, can someone help, please?

Answer 1

Maybe this one also serves your purpose:

for(k in 2:4) {
  df[k-1,k+1] <- df[k-1,as.character(df$x[k-1])] + 
              df[k-1,as.character(df$x[k-1]-1)] + 
              df[k-1,as.character(df$x[k-1]+1)]
}
df
#  A tibble: 3 x 6
# x   `1`   `2`   `3`   `4`   `5`
# <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
# 1     2    99   264    77    66    55
# 2     3    99    88   231    66    55
# 3     4    99    88    77   198    55